Thickness effect on nickel silicide formation and thermal stability for ultra shallow junction CMOS

High purity Ni films from 200Å down to 40Å on p-type Si (100) substrates are treated by rapid thermal annealing to form the metastable and stable phases of nickel silicides. The stoichiometric composition of NiSi determined by Rutherford backscattering is independent of the initial Ni thickness under 500°C annealing. Channeling RBS results reveal that the NiSi growth on Si (100) has no preferred orientation. The sheet resistance as well as surface roughness of thinner films starts to increase at a lower temperature, indicating that thinner films are thermally less stable. Agglomeration of NiSi film agrees with the grain boundary grooving model and occurs more easily within thinner films. The transformation from the NiSi phase to the NiSi₂ phase is studied by micro-Raman spectroscopy. This phase transition of thinner films begins at a lower temperature than that of thicker ones.